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Syntheses, Structures, Ionic Conductivities, and Magnetic Properties of Three New Transition-Metal Borophosphates Na5(H3O){MII3[B3O3(OH)]3(PO4)6}·2H2O (MII = Mn, Co, Ni)

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posted on 01.05.2006 by Miao Yang, Jihong Yu, Jiancheng Di, Jiyang Li, Peng Chen, Qianrong Fang, Yan Chen, Ruren Xu
Three new open-framework transition-metal borophosphates Na5(H3O){MII3[B3O3(OH)]3(PO4)6}·2H2O (MII = Mn, Co, Ni) (denoted as MBPO-CJ25) have been synthesized under mild hydrothermal conditions. Single-crystal X-ray diffraction analyses reveal that the three compounds possess isostructural three-dimensional (3D) open frameworks with one-dimensional 12-ring channels along the [001] direction. Notably, the structure can also be viewed as composed of metal phosphate layers [MII(PO4)2]4- with Kagomé topology, which are further connected by [B3O7(OH)] triborates, giving rise to a 3D open framework. The guest water molecules locate in the 12-ring channels. Partial Na+ ions reside in the 10-ring side pockets within the wall of the 12-ring channels, and the other Na+ ions and protonated water molecules locate in the 6-ring windows delimited by MO6 and PO4 polyhedra to compensate for the negative charges of the anionic framework. These compounds show a high thermal stability and are stable upon calcinations at ca. 500 °C. Ionic conductivities, due to the motion of Na+ ions, are measured for these three compounds. They have similar activation energies of 1.13−1.25 eV and conductivities of 2.7 × 10-7−9.9 × 10-7 S cm-1 at 300 °C. Magnetic measurements reveal that there are very weak antiferromagnetic interactions among the metal centers of the three compounds. Crystal data:  MnBPO-CJ25, hexagonal, P63/m (No. 176), a = 11.9683(5) Å, c = 12.1303(6) Å, and Z = 2; CoBPO-CJ25, hexagonal, P63/m (No. 176), a = 11.7691(15) Å, c = 12.112(2) Å, and Z = 2; NiBPO-CJ25, hexagonal, P63/m (No. 176), a = 11.7171(5) Å, c = 12.0759(7) Å, and Z = 2.